In recent years floating breakwater units have been developed, which utilize a series of tethered floats connected to a submerged ballast to diminish the force and size of waves generated in the water. The desirability of such a system is readily apparent when considering the protection for moored boats and ships as well as the creation of a temporary harbor or the control of beach and sand erosion. The general arrangement of such a breakwater unit consists of a large number of floats which are aligned in a series of rows and are connected through tether lines to a submerged ballast, which is anchored by cable to the bottom of the body of water. As waves hit or contact the first line of floats, the oscillation of the floats throughout the parallel lines causes a drag that absorbs energy from the waves and reduces their height.
The size of the floats as well as the ballast and the length of the tether lines are all dependent upon the partic ular locality and conditions of the water where the unit is to be placed. For instance, the size of the floats for use in a bay or harbor area may be 12 inches in diameter and the overall unit may have approximately 800 floats, with the rows being 150 feet in length. However, in an ocean system, the floats may be larger (5 to 7 feet in diameter) with the length of the units reaching 500 to 600 feet. Further, the length of the tether lines will also vary according to the height and frequency of the waves.
It is essential, however, that the tether line length for the unit be consistent throughout the floats in order to provide the uniform and most efficient operation in the absorption of wave energy to diminish the size and force of waves. The criticality of the length of the tether lines is of such importance that the tolerance is very small and the uniform length must be specifically maintained throughout the breakwater unit.
One of the major problems with respect to the overall design of the unit is the junction between the tether lines and the respective float and the ballast. It has been estimated by oceanographers that the number of waves a year that could wash over a float breakwater in a bay, for instance, would be 14,000,000. Consequently, the number of oscillations in pendulum motion between the floats and the ballast which is experienced by the junctions between the tether line and the floats and ballast is of a verny significant number, producing a great amount of fatigue and fiber abrasion on the tether line, typically resulting in the potential breakage of the line. The object of a good tether float breakwater unit is to be able to place it in locations where it can be left unmaintained to operate essentially maintenence-free over long periods of time. The fatigue and possible breakage of the tether lines through their typical knot or bolt-like attachments to the ballast and the floats pos a significant problem to the maintenance-free objective of the breakwater units.
Another advantage of the use of breakwater units relates to control of the effects of a storm, which can frequently generate 4-5 foot waves in a harbor where boats that are exposed to the main channel receive a tremendous beating and damage. The use of these breakwater units can also greatly increase the amount of shipping which can utilize a particular harbor area, as well as actually establishing a temporary harbor where none exists for loading and off-loading cargo. Furthermore, the military, especially the Navy, has an interest in such units, as they can provide a great advantage in aiding an assault landing.